The long-term goal of our work is to understand vertebrate development at the molecular level. In previous grant periods, we have characterized the activities of BMP antagonists. In the next five years, we will examine the biological roles and mechanisms of antagonists of TGF-beta 3 family members further, with a particular emphasis on their roles in organogenesis. These experiments will rely on gain of function analysis in Xenopus and loss of function analysis in the mouse. The experiments will be complemented by biochemical analysis of the mechanisms by which antagonists block BMP function.